Method for controlling heat in catalytic reactions



Oct. 2l, 1941. H. M. NELLY, JR., E-rAL 2,260,152

METHOD FOR CONTROLLING HEAT IN CATALYTIC REACTIONS Filed June 16, 1938 Hue 6d.; Pfad ef' l 550w/'afar ATTORNEY Pnemd a. 21, 1941 Henry M. Nelly, Jr.,

Rubin, Welt Caldwell, '-N. J.,

our invention reiasto a method for con trolling' heat in catalytic reactions, and more particularly to supplying heat in endothermic catalytic reactions or removing heat in exothermic catalytic reactions.

In a catalytic reaction teract in the presence of a`catalyst, the reaction proceeds initially at a -very rapid rate and retards as'eq'ullibrium is reached. Actually, the reaction is never lcompleted commercially, due to the slow .rate at which it proceeds as it reaches completion. We have observed that the rate of the reaction is not a linear function, but proceeds rapidly initially and Athen progressively decreases -to a point where the rate of reaction is very small.

in which reactants in If the reaction is endothermic, its velocity is reflected by ca loss of heat ata rate which is' a function of the velocity of the reaction.

For purposes of clarity and by way of illustration, we will describe our invention with respect to the catalytic pyrolysis of highboiling hydrocarbons to low boiling hydrocarbons, that is, with respect to catalytic cracking which is an endo-` thermic reaction, though' it is to be understood, of

lcourse, that our invention is applicable to Kcatalytic/reactions generally.

In' a-'method of catalytic cracking, oil vapors are heated to the cracking temperature and, when the heated vapors contact the catalyst, decomposition proceeds. As the reaction proceeds, if no heat is supplied, the temperature of the re actant hydrocarbons drops, with the result that the reaction willproceed less rapidly ntil a temperature is -reached 'at'which substantially no cracking willtake place., Then, too, variations vin temperature result not only-in variations in resultant decomposition productsv yieldsbut the will vary in their composition. l 'g One" object of our invention'is to provide a method for controlling heat in catalytic reactions. Another object of our invention is to provide the vapors may pass through pipe coil I1 situated asferri-:.lsu. ra mme nur nr ellogg- Company, New York, corporaion of Delaware Application yJune 1s, 193s,

2 Claim OFFICE unime americas .remy city, mi man c.

,animera `to The N.- Y., l.

a continuous method of cracking hydrocarbons with the ald of acatalyst, in such a manner as to provide maximuml yields lof uniform products'.

Other and further objects of our invention will I appear'from the following description.

In the accompanying drawing which forms part of the instant specification and is to be read in- -conjunction therewith, the flgure illustratesI a.

` diagrammatic' view of one vform of apparatus capable of carrying out the method of'pu'r invention.

Referring now to the drawing,.hydrocarbon oil to be cracked is stored in tank I 'from which it is`withdrawn through pipe 2 and pumped by pump 3 through pipe I through coil heated by convection heat, a`nd coil l0 heated by radiant heat, and positioned in afurnace `l. The oil is heated to 'vaporizing temperatures'and is `passed through transfer pipes into' a separating tower 0 in which the heated oil is flashed into vapors and unvaporized oil.A If .the transfer temperature gaat `the, desired cracking temperature, which may be between 800 F. and 950 F. gr-higher, and enough superheat has been supplied, lthe hot vaporsfrom the separator Q'through pipe I0 withdrawn lpass through pipe II and pipe I2 to a catalytic reactionIchamber' I3. If the vapors are not sumciently heated, valve I4 may be closed, in whole or in part, and valves I5 and IB opened so that in furnace I8, to .be heated to the desired tmperature.v

The unvaporized oil is Awithdrawn fromthe' separator 9 through pipe- I9 and is pumped-by $5 pump 20 through -pipe 2|i throughs. heat ex;

changer 22.*which is supplied a cooling medium, through pipe 423. All or a' portion'lof the cooled oil may be withdrawn through pipe 24 which is controlled by valve 25. If desired, valve 26 may be opened, permitting the cooled oil `to pass into a method fo'r controlliilg"heat in endothermic of the endothermic heat of reaction during the initial cracking vperiod where the rate 'of cracking and heat absorption proceeds rapidly and;

where heat addition by indirect means is' diilicult. Another object of our invention isvto provide-a -novel method for the catalytic conversion ofA highA boiling hydrocarbons carbons.

. Another object ofour into lower boiling lhydroture of the oil .passing into the `separator Sato be y the separator 9 through pipe 21 as a fluxing medium. Valve `28 controls lthe passage of cooled `oil through pipe@ 29 which discharges into `the transfer liney l enabling control of the tempera? 'easily made.' If desired, steam maybe introduced into the' separating, tower through lpipe 30. controlled by valve 3i to assisty in the sc aparationnf l the vapors from the unvaporized cih-The 'reac tion chamber may comprise a plurality of tubes i a lower tube sheet 34.

i invention is to provide "tinuously feeclixisv 32 extending between an upper tube sheet mand l A The tubes. are 'filled with finely divided catalyst 3 5 which may be of any 'suitable A pipe-Itis providedgforsconcatalyst to tne-tubesaanf desired, a spent catalyticmaterial may be con- ",.tmuously withdrawn from the tubes through pipe 31, it being understood, of course, that if a continuous catalyst replacing operation is employed, the screen 38, holding the catalytic material in the tubesis not used. If, on the other hand, stationary columns of catalytic material are employed, pipes 35 and' 31 are closed by suitable valves (not shown). 'I'he heated oil vapors introduced into the reaction chamber I3 through pipe I2. rise upwardly through the tubes 32 in contact with the catalytic material and the re- 'action products are withdrawn from the upper f ble gases are vented through pipe4 46 controlled by back pressure controlled valve 41. Water is withdrawn from the separator through pipe 48. The iinal product is withdrawn from the separator through pipe 49. Reflux passes through pipe 50 controlled by valve 5I into the fractionating tower 48 to control the top tower temperature. Reflux condensate from the bottom of the tower is withdrawn therefrom through pipe 52, controlled by valve 53. A'portion or all of the reflux condensate may be recycled through pipe 54, being pumped by pump 55 through pipe 56 into the o il passing tolthe furnace 1. A portion or all of the reiiux condensate may be withdrawn through pipe 51 controlled by valve 58. l It will be observed that a portion of the heat of cracking is supplied through the hot oil vapors which likewise is less than that between baille 54 and hame 53, which similarly is less than that between bame 64 and the upper tube sheet 33.'

The heat exchange medium may be any sul able medium. lFor convenience, we prefer to luse hot ilue gases which are produced in a flue gas' producer 65 which comprises a chamber having refractory walls 58. The chamber 88 is a mixing chamber into whichis introducedy fuel through pipe I3 controlled by valve 18, and air through pipe 1I con-trolled by valve 12, the proportions of air and gas being such as to form a combusatble mixture having the desired temperature when burned at the outlet of the producer 85. 'I'his ue gas at high temperature which is passed to the reaction chamber .through duct 14 is controlled by a 'damper 15. The upper end of the chamber I3 is connected to a stack 16 througha duct 11, the passage of gases to the stack being controlled by a damper 18. If desired, force draft may be employed by positioning an -exhaust or discharge fan at the point occupied by damper 18, it being understood that the stack and damper are the equivalent of force draft means. To `control the temperature and indirect heat transfer rate, a portion of they ue gases which have passed through chamber I3 maybe recycled through duct 19 and passed by blower 8l through duct 82 into duct 14, the amount of recirculation being controlled by the speed of the blower and damper's 80 and 83.

It will be observed that the direction of now of the heating medium and its velocity of flow is such that a maximum amounto'f heat issupplied during the first pass of the heat exchange medium. In other words, while the heat exentering the reaction chamber. In the lower porV tion of the reaction tubes 32, that is, when the hot oil vapors rst contact the catalytic material, the reaction will proceed with the greatest rapidity andif no heat be supplied, the speed of the reaction will decrease more rapidly. In accordance with the objects of our invention, i supply a portion of the endothermic heat of re-^ action as superheat in the oil vapors and a por" tion by an indirect heat exchange medium in V such manner and at such a rate vequal to the ab# sorption of heat due to the reaction. It will be' obvious from what has been said hereinbefore that vthis rate must -be` a varying one and that` heat must be supplied more rapidly during thel irst portion of the reaction tubes than at the latl.ter portion of the reaction tubes. We accomplish this result byproviding an elongated path of ow for the heat exchange medium, the heat exchange medium owing concurrently with the -ow of theoil vapors and across the tubes in such a manner that the velocity of ow of the heat exchange medium is progressivelyvdecreasing. V Referring now to ,the:drawing, it will be ob-i served that the tubes 32 of the reaction chamber I 3 are surrounded by a casing 60 of refractory material and thatthe space within the casing is divided by a plurality of bailies I,"62,` 63, and

'64,1to provide an elongated path or a heat ex v `tlwill be further observed 70 change medium. v

that the spacingofthe baiiles is not uniform but that the space between the tube-sheet- 34 and the. baille Slis less than the space between the- .b ame 8| and thebame52, which spaceinv turn, Ils less than' that between baie 82 and baille 63,

we' propose tol change medium is owlng between the tube sheetA 34 Aand the baiiie 6I, it is at the greatest temperature and is traveling with the greatest Between baiile 6I and baille 62 the temperature is somewhat reduced. However, the reaction is l proceeding in that by these bailies at' in the first portion ilarly, the heat exchange medium will at a still lower velocity and at still lower temperature between baille 63 and baille 62 but, in this portion of the reaction tubes 32, the reaction .velocity and hence the endothermic heat, is correspondingly lower. The arrangement is such that the endothermic heat of reaction is constantlv being supplied at a rate substantially equivalent to the rate of the reaction.4 Thus, the temperature of the vapors is maintained at the desired reaction their passage in contact with the catalytic maportion of the tubes embraced a rate which is less than that of the reaction tubes 32. Simterial since the endothermic heat vof the reaction is being supplied as fast as required( Before designing apparatus capable of carrying out the port and in which the reaction temperature was 850 F., the charging stock was such that a por-- endothermicy heat of the reaction' could be supplied by superheatingthe feed va'- ,tion of the be flowing' temperature throughout Vbe superneated. The temperatme of 'the heat pors 30. In 'other words, the furnace -I8 was employed to impart to the vapors a `temperature of 880 F. The first pass of the reaction chamber, that is between baille 3| and tube sheet 3l had to Supply 437,000 B. t. u. per hour which, for the design employed was 2025 B. t. u.-per hour per square foot of heat exchange surface. In a reaction chamber measuring twenty feet between tube sheets, the rst bame 8| was placed two feet above the lower tube sheet 34. The second pass had to supply 258,000 B. t. u. per hour or heat at a rate of 900 B. t. u. per hour per square foot of heating surface. To accomplish this, the baille 32 was placed three feet above the baille 3| The next pass had to supply 160,000 B. t. u. per

exchange medium may be readily controlled by recycling iiue gases and the rate of heat exchange may be also controlled by means of valves 'I2 and 1I, it being understood of course that the air and the gas supplied to pipes 69 and 1| are undenpressure.

It will be seen that we have" accomplished the objects of our invention. `We have provided a method of conducting a catalytic reaction in which the endothermic heat of the reaction is supplied at a rate substantially equal to the velocf ity of the reaction in such a manner that the hour which, for the design employed and the op` eratingconditions, was calculatedeto be 460 B. t. u. per hour per square foot of heating surface. This warohtained by placing the baille 63 four feet from bame 62. The next pass, that is between bardeand baihe 33 had to supply 95,000 B. t. u. per hour or heat at a rate of 253 B. t. u. per hour per square foot of -heating surface for the operating conditions. This was 0btained by placing the baille 34 ve feet jbaille 33.

The sixth pass, that is, between the tube sheet 33 and the baille 34 had to supply 70,000 B. t. u. per hour which, under the operating conditions' and the design employed. was calculated to be 145 B. t. u. per hour per square foot of heating surface. This was obtained by placing the baille 34 six feet below the tube sheet 33. It will be observed that six feet plus tive feet plus four feet plus three feet plus two feet equal twenty feet,

which is the distance between tube sheet 3| andv the calculated rates of 2025 B. t. u. per hour per square foot of heating surface, 900 B. t. u. per

hour per square foot of heating surface, 460- B. t. u. per hour per square foot of heating surface, 253 B. t. u, per hour per square foot of heatmg "surface, and 145 B. t.'u. perhour per square foot of heatingsurface, respectively.

An operation in accordance with our invention wasv able to crack oil continuously-,in'such manner that the endothermic heat of the reaction was substantially supplied by'the heat exchange x medium.` It will be apparentto those skilled in the art that minor discrepancies vin the rate of supplying the endothermic heat of reaction can be readily corrected by the variation in the temperature of the oil being charged to the reaction zone between certain limits. If the rate of heat exchange is too great, the oil being charged may be somewhat belowthe desired cracking temperature. If the rate of heat exchange be somewhat less tuaa that necessary to supply the endothermic heat of reaction, the oil vapors may reactant passes through the reaction zone at a substantially constant temperature, resulting in maximum yields of a uniform product.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and sub-combinations. is within the scope of our claims. It is further Y obvious that various changes may be made in details within the scope of our claims without departing from the spirit of our invention. It is,

above 25 therefore, to be understood that our invention is not to be limited to the specific details shown and described.

Having thus described our invention, we claim: l. A method of converting high-boiling hydrocarbons to lower boiling hydrocarbons which V comprises passing the high-boiling hydrocarbons in the vapor phase and at an elevated temperature in a.v plurality of conilned paths through a reaction zone comprising a plurality of aligned. columnar masses of a cracking catalyst under reaction conditions adapted to effect the desired conversion, passing a stream of a heat-exchange medium in heat-exchange relation with the reaction zone in a winding confined path traversing and retraversing saidcolumnar masses and progressively increasing the cross-sectional area of said stream thereby progressively decreasing the velocity of ilvow thereof, the progressive increase in cross-sectional area being effected in a direction and being of a magnitude adapted to maintain the reaction zone at a proximate optimum temperature.

2. A method of converting high-boiling hydrocarbons to lower boiling` hydrocarbons which comprises passing the high-boiling hydrocarbons in the vapor phase and at an elevated temperature in a plurality of conned paths through a reaction zone comprising a plurality of aligned,

columnar'masses of a cracking catalyst under re- Aaction ,conditions adapted to effect the desired conversion. passing a stream of a heat-exchange medium in heat-exchange relation withV the reaction zone in a winding conned path traversing Y and retraversing said columnar masses. said hydrocarbon vapors and heat-exchange medium being introduced at the same end of said reaction zone and withdrawn at the opposite end thereof, and the cross-sectional area of said stream of 'heat-exchange medium being progressively increased in the direction-of movement of saidA stream.

` HENRY M. NELLY, Jl.

LOUIS C. RUBIN.-

This is contemplated by and 

